<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <script>
        const Π = 3.14159265
        var r = 2
        var area
        var l
        l = 2*Π*r
        area=Π*r**2
        console.log("l="+ l)
        console.log("area=" + area)
        var a=1
        var b=2
        var c
        c=a
        a=b
        b=c
        console.log("a="+ a)
        console.log("b=" + b)
        function f() {
            var name = "李兆康"
            var age = 18
            var address = "河北省"
           alert("我的名字"+ name + ", 年龄是" + age + ",住在"+ address)
        }

    </script>
    <button onclick="f()">点击</button>

</body>
</html>